Why can't nested describe() blocks see vars defined in outer blocks?

Question

I\'ve run into this issue in real code, but I put together a trivial example to prove the point.

The below code works fine. I\'ve set up a variable in my root desc

Answer 1

The body of a describe block is executed before the beforeEach blocks.

This is exactly as expected. The problem is that your var trees variable is trying to access orchard before it has been initialized. The body of a describe block is executed before the beforeEach blocks. To solve this problem, the third code snippet is the only way to go.

Jasmine will first execute the describe blocks, and then execute the beforeEach blocks before running each test.

Answer 2

Lets take the third code snippet. Further, it can be refactored as below:

describe('simple object', function () {
    var orchard;

    beforeEach(function () {
        orchard = {
            trees: {
                apple: 10,
                orange : 20
            },
            bushes: {
                boysenberry : 40,
                blueberry: 35
            }
        };
    });

    describe('trees', function () {

        it ('should have apples and oranges', function() {
            expect (orchard.trees.apple).toBeDefined();
            expect (orchard.trees.orange).toBeDefined();

            expect (orchard.trees.apple).toEqual(10);
            expect (orchard.trees.orange).toEqual(20);
        });
        it ('should NOT have pears or cherries', function() {
            expect (orchard.trees.pear).toBeUndefined();
            expect (orchard.trees.cherry).toBeUndefined();
        });
    });
});

For the new comers to Jasmine, this is how you intrepret the above code :\

1. describe defines a test suite. The test suite name here is a user defined simple string, say "simple object".
2. A test suite can itself contain other test suites, meaning describecan contain nested suites.
3. Just like other programming languages, orchid is global to all the functions & suites defined within simple object test suite.
4. It block is called a specification or a SPEC. It blocks contain individual tests.
5. Just when Jasmine executes the test cases, it will first visit the it blocks meaning it will traverse all the it block declarations.
6. When Jasmine actually executes test cases, it will check for beforeEach function and hence orchard gets trees value assigned to it.

7. And hence you need not write a beforeEach function, inside a sub suite. You can simply ignore

   beforeEach (function() { trees = orchard.trees; });

8. Now compare the latest snippet below with the third snippet above.

Answer 3

Well you could still initialize variables outside the beforeEach block. I generally do it for constants and still remain DRY without introducing beforeEach blocks.

describe('simple object', function () {
    const orchard = {
        trees: {
            apple: 10,
            orange: 20
        },
        bushes: {
            boysenberry: 40,
            blueberry: 35
        }
    };


    describe('trees', function () {
        const trees = orchard.trees;

        it('should have apples and oranges', function () {


            expect(trees.apple).toBeDefined();
            expect(trees.orange).toBeDefined();

            expect(trees.apple).toEqual(10);
            expect(trees.orange).toEqual(20);
        });
        it('should NOT have pears or cherries', function () {
            var trees = orchard.trees;

            expect(trees.pear).toBeUndefined();
            expect(trees.cherry).toBeUndefined();
        });
    });
});